1. Field of the Invention
The present invention relates to an image display apparatus and method capable of suppressing a “motion blur” without changing the gradation.
2. Description of the Related Art
Recently, various apparatuses equipped with image display means, including a TV receiver and PC monitor, have been put into practical use. As these image display means, various devices such as a liquid-crystal display apparatus are used. For example, the liquid-crystal display apparatus adopts a method of adjusting a constantly emitting backlight by a liquid-crystal shutter, and outputs light in every 1-frame period throughout the 1-frame period. Thus, the liquid-crystal display apparatus is called a hold-type display apparatus. When pursuit of a moving image (viewing of tracking a moving portion with a line of sight on a moving image display) is performed on the hold-type display apparatus, a “motion blur” corresponding to the light output period is observed. In a 60-Hz moving image display, a minimum of 16.7-ms “motion blur” is observed in principle.
As a technique for reducing the “motion blur”, there is proposed a method of changing an input image having a 60-Hz frame rate to have a 120-Hz double frame rate, increasing the spatial high frequency component of the image in one subframe, and decreasing it in the other subframe. In a technique disclosed in Japanese Patent Laid-Open No. 2006-184896, the perception of the edge of an image is made close to the impulse type by shifting the center of gravity of the display time of the spatial high frequency component. Also, in the technique disclosed in Japanese Patent Laid-Open No. 2006-184896, an increase and decrease in spatial high frequency component are canceled between subframes. When an image is viewed at a frame rate of 60 Hz, a decrease in luminance, that is, a change of the gradation can be prevented.
When calculating an image whose spatial high frequency component is increased, the calculated gradation may deviate from a displayable gradation (underflow/overflow). If an underflow/overflow occurs in an image whose spatial high frequency component has been increased, an increase and decrease in spatial high frequency component cannot be canceled, and the gradation changes in the corresponding pixel. It is ideal to suppress a “motion blur” without changing the gradation. It is therefore necessary to adjust the decrease amount of the high frequency component so that an image whose spatial high frequency component has been increased falls within the displayable gradation.
In Japanese Patent Laid-Open No. 2006-184896, the high frequency component is adjusted, so that the number of gradations of an image whose spatial high frequency component has been increased becomes equal to or smaller than the maximum number of gradations in order not to change the gradation. However, if the high frequency component is decreased uniformly, the “motion blur” suppression effect may degrade. Also, an image whose spatial high frequency component has been increased may become equal to or smaller than 0 gradation (underflow). However, this is not especially an issue in Japanese Patent. Laid-Open No. 2006-184896.